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Spring Over Axle On A Amc 20 Mj


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Has anyone ever done this? I have an 86 MJ with an AMC 20 axle and I'm looking for a little extra lift to match the rear. SOA seems like the way to go. Rocky Road sells a kit that is entirely bolt on, but they only have options for the D35 and 44 (http://www.rocky-road.com/jeep-comanche-lift-kit.html) Will this still work? 

 

Thanks for any input,

Reilly

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Avoid that kit at all costs. You can get cheap factory style perches or high quality longer ones from Barnes or Ruffstuff. It just requires a touch of welding. The AMC has 3" tubes IIRC and not 2.75" like the other MJ axles.

 

A simple swap kit from Barnes 4wd gets you a great & complete kit that is much beefier than stock.

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Scratch that, I found a pair of 3" on rough stuff. Thanks for the info!

 

Anyone one have any advice on doing the swap? Hows the ride afterwords?

The ride doesn't change, because you don't change the springs. If you change the shock absorbers, any change in the ridge will be caused by what shocks you choose.

 

However ... your opening post says you are looking for "a little" extra lift. How much lift do you want? The minimum you get from a SOA is 5-1/2 inches. Do you need that much?

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Yeah I figured I would pull a leaf to compensate. The truck has an older lift on it, 3" coils and a 2.5" add-a-leaf; the coils are holding up great but the leafs are old and tired. I'd say the sag is about 2" lower in the rear compared to the front. If I pull the helper spring and then SOA it, then I should be at about 3" of total lift. That's my thought, anyway haha. We'll see if it works out that way. 

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Yeah I figured I would pull a leaf to compensate. The truck has an older lift on it, 3" coils and a 2.5" add-a-leaf; the coils are holding up great but the leafs are old and tired. I'd say the sag is about 2" lower in the rear compared to the front. If I pull the helper spring and then SOA it, then I should be at about 3" of total lift. That's my thought, anyway haha. We'll see if it works out that way.

Why don't you measure the actual rear ride height before doing anything, then you'll have a better idea of how to get from where you are to where you want to be. For that matter, also measure the front so you'll know if your 3" coils are really giving you 3" of lift. How to measure the ride height has been discussed here several times recently.

 

Frankly, going to the trouble of doing a spring-over conversion and then removing a leaf from weak, sagged springs in the hope that the SOA conversion will result in 3" of lift rather than 6" of lift seems to me like a bad bargain. If your springs are that bad, I would just get a new AAL or get a pair of new, custom springs to put the ride height where you want it. You're going to go through all that work, and then your springs could break next week.

 

[Edit to add] I found one of the posts explaining how to measure:

 

COMANCHE STOCK HEIGHT

 

Front: Measure from top of axle tube to underside of frame rail, inboard of the coil spring. Do NOT measure from the diff housing or shift motor housing. 2WD models should be 6-3/4" plus or minus 1/2". 4WD models should be 7-3/4" plus or minus 1/2".

 

Rear: Measure the vertical distance between the top of the axle tube and the underside of the frame rail inboard of the jounce bumper. 2WD models should be 8.2" plus or minus 1/2". 4WD models should be 9.2 inches plus or minus 1/2".

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